Francisella tularensis Subspecies holarctica, Tasmania, Australia, 2011

Justin Jackson, Alistair McGregor, Louise Cooley, Jimmy Ng, Mitchell Brown, Chong Wei Ong, Catharine Darcy, and Vitali Sintchenko

Author affiliations: Royal Hobart Hospital, Hobart, Tasmania, Australia (J. Jackson, A.R. McGregor, L. Cooley, C.W. Ong, C. Darcy); Westmead Hospital, Sydney, New South Wales, Australia (J. Ng, M. Brown, V. Sintchenko); and The University of Sydney, Sydney (V. Sintchenko)

Abstract

We report a case of ulceroglandular tularemia that developed in a woman after she was bitten by a ringtail possum (Pseudocheirus peregrinus) in a forest in Tasmania, Australia. Francisella tularensis subspecies holarctica was identified. This case indicates the emergence of F. tularensis type B in the Southern Hemisphere.

Figure 1

Thumbnail of Ringtail possum (Pseudocheirus peregrinus) as photographed by its bite victim, Tasmania, Australia, 2011.

Figure 1. . . Ringtail possum (Pseudocheirus peregrinus) as photographed by its bite victim, Tasmania, Australia, 2011.

Tularemia is a zoonosis affecting a wide range of wildlife species, including mammals, birds, amphibians, and arthropods (1,2). Three subspecies. of Francisella tularensis have been recognized as causes of disease in humans: ssp. tularensis (a cause of type A tularemia), ssp. holarctica (a cause of type B tularemia), and ssp. novicida. Type B tularemia is endemic to the Northern Hemisphere, and cases predominately occurring in latitudes 30°N–71°N (1,2). We report a case of ulceroglandular tularemia in a human in Tasmania, Australia (latitude 42°S) who was bitten by a ringtail possum (Pseudocheirus peregrinus, Figure 1).

The Case

In February 2011, a 44-year-old woman was bitten on her right index finger by a wild ringtail possum near the Henty River on the western coast of Tasmania. The incident occurred in daylight, and the possum, normally nocturnal, appeared lethargic and unwell. The patient was immunocompetent and had never traveled outside of Australia. Three days later, an ulcer developed at the site of the bite, followed by the development of swollen and tender epitrochlear lymph nodes, fever, rigors, myalgias, and drenching night sweats. On day 4, the patient was prescribed oral β-lactam antimicrobial drugs by her local doctor. She took these for 2 weeks without clinical improvement. Axillary lymphadenopathy was palpable on day 14, and by day 17 the epitrochlear nodes had formed a spontaneously discharging sinus. A swab sample was collected from the primary ulcer site on day 17. No organisms grew after a 48-h incubation at 36°C in the following culture media: blood agar in ambient air, MacConkey agar in ambient air, and chocolate agar in 5% CO₂. The patient’s antimicrobial drug regimen was altered empirically to ciprofloxacin 500 mg 2×/day and amoxicillin/clavulanic acid 875 mg/125 mg 2×/day for the next 4 weeks. Despite mild improvement in symptoms, epitrochlear and axillary lymphadenitis with suppuration persisted. Swab samples collected for fungal and mycobacterial culture from the epitrochlear sinus on day 30 were culture negative. On day 47, the patient was referred to the Royal Hobart Hospital in Tasmania. Histology from an excisional biopsy of the epitrochlear sinus on day 50 revealed acute inflammation and a few non-necrotizing epithelioid granulomas. This tissue and an axillary lymph node aspirate were sent to a reference laboratory for molecular studies.